The present invention relates to compounds and derived materials which are capable of undergoing substantial changes in their optical properties in response to environmental changes, namely, compounds and derived materials which, for example, undergo substantial changes in their optical emission, absorption, and refraction in different environments. In addition, the subject compounds and materials conveniently may be fabricated into optical device and circuit configurations by conventional photo processing techniques. Such devices and circuits are highly useful, for example, in a variety of applications, including computer, telecommunication, entertainment, defense, and sensor applications.
An example of such devices include biomedical sensors, such as, a non-invasive glucose analytical system and an extremely high frequency, that is, EHF=3 GHz to 3 THz, electrooptical modulator. The former biomedical sensor is sensitive in its optical emission with respect to the levels of glucose in the surrounding environment. The latter electrooptical modulator is sensitive in its index of refraction with respect to the electric field strength and direction in the surrounding medium.
A major subclass of the subject compounds and materials are capable of optical emission, absorption, and strong refraction in that region of the long wavelength visible and short wavelength near infrared spectrum from 800 nm to 1200 nm wherein human blood and tissue possess minimal optical absorption. Therefore, such compounds and materials may be used with implants for non-invasively determining vital medical information, such as blood and tissue levels of glucose, electrolytes, heavy metals, carbon dioxide, oxygen, antibodies, acidity, and/or alkalinity, and the like. In addition, within this wavelength range, there now exists a very broad range of compact and low cost optical transmitters and receivers which permit complete diagnostic systems to be mass produced at low cost and conveniently carried by the consumer
As an example of the timeliness and utility of this invention, we illustrate its advantages over a state-of-the-art glucose analytical system. In a recent book cited below, a glucose analytical system was proposed using the environmentally sensitive Texas Red material. This system, due to limitations imposed by the optical absorption of Texas Red in the wavelength range 500 nm to 600 nm, utilized an optical transmitter consisting of a green helium neon gas laser with a 543 nm emission line. This laser, which is very expensive, large in size and requires a large power source, precluded the application of this system as a low cost, portable, user-friendly device. In addition, high absorption of the 543 nm line by human skin, hemoglobin, and oxyhemoglobin encourages the discovery of environmental sensors which absorb light from optical transmitters which emit in the wavelength range of 800 nm to 1200 nm; a broad range of subject compounds and materials of the present invention absorb in that wavelength range.
Currently, in the wavelength range of 800 nm to 1200 nm, a number of compact, low cost LED's and laser diode optical transmitters and a number of PIN and photodiode optical detectors now exist. Therefore, compositions of matter which are active in this range fill a current vital need, as they may be used as environmental sensors in conjunction such transmitters and detectors.
There exist current, state-of-the-art environmental sensor compounds for biomedical applications for implant use; these compounds are designed to possess optimum absorption and emission properties in the long wavelength visible or short wavelength region of 650 nm to 1200 nm to function efficiently in the presence of human skin, hemoglobin, and oxyhemoglobin which together have low absorption above 700 nm and minimal absorption between 1000 and 1200 nm. Examples of such modern materials are indocyanines which absorb near 700 nm and emit near 770 nm and naphthocyanines which absorb near 772 nm and emit near 780 nm. However, the indocyanines, apparently due to the presence of multiple single bonds within the conjugated center of the molecule, are inefficient emitters due to rotation around these bounds which lead to quenching of luminescence. The naphthocyanines are highly insoluble materials and are therefore difficult to incorporate into devices and systems. In addition, the naphthocyanines are highly stable to light and therefore not readily photoprocessable. Both the indocyanines and naphthocyanines fall short in both absorption and emission of the long wavelength range of 800 to 1200 nm preferred for biosensors.
Preferred compositions of matter should involve chromophores which embody the conjugated portion in a totally rigid, planar structure in which the single bonds cannot rotate about their axis in a manner to interrupt conjugation. Therefore, such compounds and derived materials are likely to be more efficiently luminescent than their cyanine or merocyanine counterparts, such as the indocyanines described above, which contain deleterious, rotatable single bounds, the rotation of which can break the conjugation and thereby cause emission to occur at low efficiency. In addition, preferred compounds and materials should absorb and emit in the highly preferred 700 to 1200 nm wavelength range.
To be practical and broadly applicable such compounds and materials should be producible by highly conventional, modular chemistry which during the appropriate processing steps can be rendered in highly soluble or liquid form; thus, they may be readily incorporated into devices or systems. In this regard, such compounds and materials have advantages over the naphthocyanines.
Luminescent biosensors and other luminescent environmentally sensitive compounds, materials, devices, and systems are discussed at length in a recent book on this topic published in 1994 by Plenum Press of New York and London entitle: "Topics in Fluorescence Spectroscopy, Volume 4, Probe Design and Chemical Sensing."
Besides biomedical applications, the present invention finds utility with regard to computer, telecommunications, entertainment, defense, and sensor systems. With an ever-increasing demand for faster performing systems in these areas, current interest has focused on materials from which such devices and systems in the extremely high frequency (EHF=3 GHz to 3 THz) range can be cheaply and efficiently fabricated.
Examples of the most simple EHF devices or components are electrooptical modulators or switches which are based on materials which undergo substantial changes in their refractive indices in the presence of applied electric fields. Currently, such EHF products are produced from inorganic crystals, such as lithium niobate or inorganic semiconductor materials, such as gallium arsenide. Devices, components, and systems for these materials are not producible at high volume, high production rate and low cost. In addition, these products are only available in quantity in the low end of the EHF ranges less that 20 GHz.
In contrast to the inorganic materials, organic polymeric materials appear to have great potential for high volume, high rate, and low cost production. Such materials may be mass produced by simple polymer coating technology in a manner resembling printing. Thus, there is a current interest in organic materials capable of manipulation of light in optical and fiber optic devices and systems. For example, such materials are the subject of an article published in the March 1996 issue of Chemical & Engineering News entitled: "Devices Based on Electro-optic Polymers Begin to Enter the Marketplace."
However, the molecular structure of the materials from which these organic polymeric EHF products are currently being produced are far from optimal. The solvatochromic spectral shifts of the compounds, azobenzene and stilbenes, responsible for the electrooptical activity of these materials are small, indicating that the electrooptical performance of derived devices and systems is likely to be small. In addition, some of the end-product materials are fabricated by an isocyanate cross-linking process which produces materials which are moisture sensitive and therefore degrade in performance over time.
Compounds and materials which possess much larger solvatochromic spectral shifts that state-of-the-art azobenzene and stilbene analogs and are therefore likely to be more electroactive. In addition to being amenable to isocyanate processing, compounds and materials that are amenable to processing techniques which do not possess moisture sensitivity problems are preferred.
Generally, materials which exhibit strong electric moments and electrooptical coefficients such as .mu.,.alpha.,.beta., and .gamma. for the compounds and X.sub.0, X.sub.1, X.sub.2, and X.sub.3 for the materials are preferred. It is well known in the state of the art that materials with high X.sub.2 are capable of producing modulation of light at high frequencies by application of appropriately modulated electric fields and that materials with high X.sub.3 are capable of producing similar modulation with appropriately modulated photonic fields. Also preferred are materials that exhibit this useful property in the near infrared range from 700 nm to 2000 nm, wherein a number of low cost coherent light sources and sensitive electronic detectors are readily available. In addition, to greatly facilitate the incorporation of these compounds and materials into environmental sensors and optical devices and systems, compounds and materials which are generally amenable to currently available photoprocessing technologies utilizing mass fabrication of these products are preferred. Therefore, the present invention relates to compounds and derived materials which, in addition to their environmentally sensitive luminescence, are able to convey and manipulate light in optical and fiber optic devices and systems as are required for extremely high frequency (EHF=3 GHz to 3 THz) computer, telecommunications, entertainment, defense and sensor applications.